Induction furnace



W. ROHN.

INDUCTION FURNACE.

APPLlCATlON FILED DEC. 21, 1920.

, 1,431,686, Patented Oct. 10, 1922.

Patented Oct. 10, 1922.

UNITED STATES wILiiELM noun, or HANAU, GERMANY.

INDUCTION FURNACE.

Application filed December 21, 1920. Serial No. 432,308.

To all whom it may concern:

Be it known that I, Dr. VVILHELM RoHN, chemist, a citizen of Germany, and resident of Hanan, Germany, have invented new and useful Improvements in Induction Furnaces, (for which I have filed applications in Germany, May .19, 1920; Sweden, July 30, 1920; Norway, September 11,. 1920; C'zecho-Slovakia, July 24;, 1920), of which the following is a specification.

Electric induction smelting furnaces described in patents and scientific publications as well as thoseused in the industry, make use of the discovery that by passing a sufiiciently strong electric current, metals can be made red hot and even heated to the point of melting, so that in that way a heat ing sufiicient for carrying out metallurgical processes, can be obtained. In order to melt in that way any considerable quantities of metal and to obtain favourable conditions from the point of view of heat utilization, the material to be melted used to be given a comparatively large cross-section, and therefore it was necessary to use extraordinarily great strength of current at low voltage. It has been therefore attempted to use constructions in which the material to be melted was introduced into a channel which was closed in itself, and the said channel was arranged direct as a secondary coil of a transformer, that is to say the primary current flowed round an iron core, which passed through the center of the melting channel while the secondary current is generated in this channel.

Although such furnaces have been extensively used in practice, they have the following important disadvantages:

A. The efiiciencyfactor cos q; is very unfavourable. The reason of this must be looked for in various circumstances, that is,

1) In the fact that the distances from the melting channel to the primary coil and to the transformer core become unfavourably great. This results in the dispersion of the transformer being great, and in the coupling between the primary coil and the secondary coil (i. e. the melting channel) being very loose. In such a transformer, even with the secondary coil short-circuited, the inductance of the primary coil is not small enough, and consequently there remains a large wattless load. As however, the machine in stallations have to be dimensioned for available eifect plus wattless efi'ect, the working of such a furnace requires a current-generating installation two to three times larger than would be required for the available efi'ect alone.

(2) In the usual constructionsthe transformer cores and the yokes connecting the same, are unfavorably arranged and too large. In that way the path of the lines of force in the transformer iron becomes comparatively too long which also results in an increase of dispersion and of losses through hysteresis.

B. The screening against the inductive action outwards of the surface of the transformer core is insufiicient. In the usual constructions the primary coil is screened outwards only in a very inadequate manner so that in all metal parts surrounding the furnace (more particularly in the parts of the furnace casing or jacket) are induced con siderable eddy currents which lead to inconvenient heating and losses of energy.

C. The rolling motion of the metal bath is very considerable and disturbing. Owing to the usual arrangements of the primary coil and the meltingchannel relatively to each other, the bath surface takes up an oblique position in the melting channel, and the material to be melted. makes rolling movements which lead to a destruction of the channel walls.

The above mentioned disadvantages are partly avoided, and partly limited to a considerable extent, by the construction of the furnace according to the present invention.

The furnace is diagrammatically shown in the accompanying drawing.

Figure 1 is a vertical section through the furnace,

Figure 2 is a horizontal section, 4

Figure 3 shows a horizontal section through another construction of the transformer iron. 1

A is the melting channel, for instance a circular one. It is closely surrounded on all sides by the primary winding B. The primary winding B is in its turn surrounded by the transformer iron C. The transformer iron is constituted by ring shaped (circular, square or the like) sheet metal plates which surround the primary winding and are arranged in a fanlike manner. The body of the transformer iron may beassumed in a way to have been produced by a suitably shaped ring of transformer plate, the plane of which passes throughthe axis of sympassing through it stituted by water cooled tubes.

metry of the circular melting channel, being rotated around the said axis. In that way a transformer iron will be produced constituted by a closed annular tube. It is immaterial whether, in accordance with the plan in Fig. 2, the single plate-rings forming the yoke, are all exactly radial, squared out only at the points of the charging and tapping holes, or whether they are combined together to form single sub-units in accordance with Fig. 3. The intermediate space between the melting channel and the primary winding is filled in a known manner with refractory material.

In the construction described, the whole of the heat radiated by, and carried away from, the metal bath, after passing through the refractory material, strikes the primary winding. The latter must be therefore sufficientlycooled. This may be done for instance by making the primary winding not of solid round copper but of a tube (owing to which the eddy currents produced in the same, are at the same time considerably reduced) and by cooling the said tube by cooling water, re-cooled oil or cooling air. In that way the winding itself is maintained cool, and at the same time the transformer iron and the furnace jacket are protected from heating.

In such a furnace construction the described disadvantages of the usual and well known constructions are reduced or avoided owing to the fact (a) That the primary winding B is con- This makes it possible, considerably to reduce the distance of the winding from the metal bath.

(b) That the transformer iron surrounds the metal' bath along the shortest possible path. In that way the path of the magnetic lines of force is considerably shortened.

Both arrangements are eminently adapted 'to limit the disadvantage set forth under A (1) and (2) and thereby to improve the cos q).

the known inductive action which in the usual constructions is exercised on the whole surrounding of the melting furnace (disadvantage B) can be practically eliminated owing to the transformer iron surrounding Moreover, owing to the newarrangement,

onlall sides the primary and the secondary co1 In that way it is possible to obtain entirely new working conditions for such furnaces and to make use of newmelting processes. By eliminating the inductive action on the fittings or on the constructive enclosure of the furnace, as well as on all the metal parts surrounding it, it becomes possible for instance to place such a furnace with its fittings into a practically gas-tight chamber. The interior of the said chamber can then be filled with any desired gases,

. and the melting and casting processes carried out under any desired adjustable excess of pressure or depression or in a vacuum and at any desired temperatures and finally can ,be carried on for any desired length of time.

Finally, the new arrangement makes it possible to eliminate completely the known injurious rolling movements of the metal bath (disadvantage C) owing to the primary coil surrounding the melting channel uniformly on all sides.

Claims:

1. Aninduction furnace consisting of an annular melting-channel which is surrounded on all sides also above as well as below the channel by the primary coil and both the melting channel and the primary coil are surrounded on all sides by annular shaped transformer iron.

2. An induction furnace as set forth in claim 1 wherein the primary coil consists of tubes which may be cooled by suitable In testimony, that I claim the foregoing as my invention I have signed my name this 20 day of February 1922.

DR. WILHELM ROHN. 

